Piston and insert ring therefor



Sept. 9, 1958 F. E. SMITH ETAL 2,851,318

PISTON AND INSERT RING THEREFOR Filed May 14, 1956 2 Sheets-Sheet 1 INVENTORS EVERETT G. FAHLMAN FORREST E. SMITH m *Q -W ATTORNEYS I P 9, 1953 F. E. SMITH ETAL 2,851,318

PISTON AND INSERT RING THEREFOR Filed May 14, 1956 2 Sheets-Sheet 2 INVENTO EVERETT G. FAHLM Y FORREST E. SMITH Evw L (Q-LM ATTORNEYS Fatented Sept. h, 1958 PISTON AND INSERT RING THEREFOR Forrest E. Smith, West Richfield, and Everett G. Fahlman, Medina, Ohio, assignors to The Permold Company, Medina, Ohio, a corporation of Ohio Application May 14, 1956, Serial No. 584,515

12 Claims. (Cl. 309-14) This invention relates to aluminum and similar soft metal alloy pistons in which a grooved band of cast iron or similar harder metal is provided in the head of the piston as a carrier band to carry the uppermost piston ring.

In the high speed, heavy duty, internal combustion engines, the heads of the pistons are subjected to a relatively great amount of heat which is desirably conducted to the more readily cooled piston skirt. Also, the steel piston ring in the upper groove of the piston head frequently tends to widen its groove by a hammering and abrasive action on the side walls of the groove, thereby reducing the effectiveness of the seal and shortening the life of the piston. To eliminate this latter ditliculty, aluminum alloy pistons have sometimes been provided with a carrier band of iron embedded in the piston head and grooved to receive a piston ring. Such carrier bands, being of greater strength and hardness and being more heat resistant than the aluminum of the piston body, are able to withstand the hammering and abrasive action of the piston ring, but there are certain difiiculties incident to the casting of the piston with the iron band embedded in the body of the piston. Also, the fact that the ferrous alloy of the carrier isa poorer conductor of heat than the aluminum body tends to impede the transfer of heat from the piston head to the cylinder wall and to increase the temperature to which the piston head is heated in service.

When a carrier band is employed which has a coeflicient of expansion materially different from that of the alloy forming the body of the piston, severe stresses are imposed at the interface between the carrier band and the metal of the body of the piston during heating and the above mentioned stresses and which will provide a minimum resistance to heat transfer downwardly from the head of the piston past the carrier band.

A further object of the invention is to accomplish the foregoing objects without the expense of employing special bonding techniques or an expensive, hard metal alloy for the carrier band.

The foregoing objectives are accomplished in accordance with the invention by employing a piston ring carrier band blank of generally annular form having a circumferential array of spaced, scallop-like depressions extending into the blank from the upper and inner surfaces of the annulus and a second similar array of depressions extending into the blank from the lower and inner surfaces of the annulus, the two arrays of de pressions being circumferentially staggered relative to each other, but in closely spaced relationship and having axial and radial depths more than half those of the annulus. An initial circumferential groove may also be provided in the outer circumferential surface of the annulus at the location of the final piston ring groove, but should be of lesser width and depth so as to leave sufiicient metal for final machining of the piston ring groove. The initial groove may or may not pierce through the ring into the scallop-like recesses. Preferably, upper and lower circumferential arrays of riblike protuberances extend respectively upwardly and downwardly from the upper and lower surfaces of the blank, the upper ribs being staggered relative to the upper array of depressions, and the lower ribs being staggered relative to the lower array of depressions and providing a rib betwen each adjacent pair of upper and lower depressions.

Such a blank contains a minimum amount of metal which can impede heat transfer and a multiplicity of upper, lower, and inner surface irregularities for interlocking with the metal of the piston body. When the blank is cast with an initial circumferential groove therein, mold pins, a mold band, or other suitable locating and supporting means carried by the mold may project into the groove to support the blank in the mold during casting of the metal of the body of the piston about the blank.

After casting such a blank in a piston, final cutting of the piston ring groove to its final width and depth pierces the blank in a radial direction opposite each upper and lower scallop-like depression, thus eliminating metal of the blank originally separating the bottom of the preliminary groove from the innermost depth of each of the depressions. As a result, circumferentially spaced upper, inner, and lower portions of the piston ring groove actually cut into and are bounded by the metal of the having the same or a closely similar coefficient of expansion as the metal of the body of the piston. Both of the above expedients, however, materially increase the cost of the piston, and the former is of dubious effectiveness for its intended purpose.

Various mechanical interlocking arrangements have also been provided for assisting in resisting the above described stresses, but heretofore these mechanical interlocks have either been inadequate alone toresist such stresses, or the mass of carrier band metal of relatively low heat conductivity has imposed an objectionable barrier to heat transfer downwardly through the wall of the piston from the hot head portion thereof.

The objects of the present invention are primarily to provide a soft metal alloy piston having a piston ring carrier band cast therein which may be made of an inexpensive cast iron or the like, yet which is so designed that it will be mechanically locked in the metal of the body of the piston so securely as to successfully resist body of the piston, providing good heat transfer between the piston ring and the body of the piston.

The foregoing and additional objects, advantages, and

characteristic features of the invention will be more fully understood from the following detailed description of the presently preferred forms of the invention, taken in conjunctionwith the accompanying drawings, in which:

Figure 1 is a perspective view of a piston ring carrier band in the finished condition as it exists after being embedded in a cast piston and after the cast. piston and original carrier ring blank have been machined and finish-ground together;

Figures 2 and 3 are fragmentary, vertical, sectional views of the finished carrier band of Figure 1, the planes of the sections being respectively indicated by the lines 2--2 and 3-3 in Figure 4;

Figure 4 is a plan View (either top or bottom) of the finished carrier band of Figure 1;

Figures 5 and 6 are fragmentary, vertical, sectional views of a finished piston having the finished carrier band of Figure 1 embedded therein, the planes of the sections corresponding, respectively, to the planes of the sections of Figures 2 and 3;

Figure 7 is a plan view (either top or bottom)- of a carrier band blank in its original cast condition while supported in a piston mold (not shownlprior to casting the piston therein, a number of locating pins also being shown in their relationship with the'blank for supporting it in the piston mold during casting of'th'e'piston;

Figure 8 is a fragmentary vertical sectional view of the carrier band blank of Figure 7, the plane'o'fthe section being indicated by the line 88 in Figure 7; and

Figure 9 is a fragmentary, vertical sectional view of a piston, as cast, and while still supported in the mold (not shown), with the carrier band blank of Figures 7 and 8 embedded therein.

Referring to the drawings, the final piston ring carrier band, generally designated 10, is preferably formed by casting an annular blank of the configuration shown in Figures 7 and 8, mounting the blank in a piston mold, pouring the piston metal so as to embed the blank in the rough cast .piston, and then machining the piston ring groove in the blank to its final dimensions and machining and/or grinding the .pistonand blank to their final outside dimensions. When such a procedureis followed, the resulting-piston ring carrier band, as it exists in the finished piston, is as separately portrayed in Figures 1- 4. The stippled surfaces in these figures are the roughcast surfaces of the original blank, and the nonstippled surfaces are those resulting from the machining operations after the piston has been cast with the blank embedded therein.

As shown inFigures '1-4, the final carrier band is of generally annular configuration, and is circumferentially continuous or uninterrupted except for spaced depression and protuberances that provide a repeating pattern of cross-sectional changes about the annulus. A circumferential array of uniformly spaced, scallop-like depressions 11 extend radially'and axially into the band from the inner surface 12 and top surface 13 thereof, and an identical array of uniformly spaced, scallop-like depressions 11 similarly extendinto the band from the :inner surface 12and bottom-surface 14 thereof. One-of these arrays of depressions 11 is circumferentially staggered relative to the other, and thedistances between the depressions 11 in each :array are :greater in -circurnferential-extent than thedepressions themselves, as'most clearly shownin Figure 4. p

The minimum-axial depth-of each depression 11=is at least as great as, and preferably slightly greater than,

one-half the axial thickness of the band between the top and bottom surfaces .13 and 14 thereof, and this depth increases uniformly in a radially inward direction to around three-quarters or more of this axial thickness at the inner surface '12 of theband. Thus, what may be termed the bottom .16 (Figures and 6) ofaeach depression 11 is inclined to the planes of the topand bottom surfaces 12 and13 of .the band at anangleof about 15 to or so, preferably about 20?. The radial depths of the depressions .11 are defined .byrg'enerally .cylindrical side walls givingathem scallop-like configurationsin a common plane normal to theaxis of-the band. The maximum radial dimensionof each depressionsllsis approximately two-thirds, more or less, of .theradial width of the band.

The final machined dimensions-of a-piston=ring..groove 17 are such that this groovepierces .the bodyof .the band '10 in a radial direction over .asubstantialpart of the circumferential extent of eachrdepression; 11-, ,providing an, opening 18 between each-.depression- 11.and-the groove 17.

A-circumferential array of uniformly spaced, .ribrlike protuberances 21 extends axially -or upwardly from-the top surface 13 of the band 10, and an identical array of uniformly spaced protuberances 21 extends axially or downwardly from the bottom surface 14 thereof. Each of the ribs 21 is disposed and extends between an adjacent pair of depressions 11 in one of the arrays of depressions in circumferential alignment therewith and is substantially aligned axially with the outer, shallow portion of one of the depressions 11 in the other array of depressions. Preferably, one of the protuberances 21 extends circumferentially between each adjacent pair of the depressions 11 in each array thereof over a substantial part of the circumferential distance therebetween, and each protuberance 21 extends axially a distance approximating the maximum axial depths of the depressions 11.

As embedded in a piston 22, the carrier band 10 preferably has its outer diameter machined down to slightly less than the outer diameter of the piston to prevent contact of the hard carrier band with a cylinder wall. The outer surface of the band is thus substantially, but preferably not quite, flush with the outer surface of the pis-' ton. Each depression 11 is filled with metal of the body of the piston, and each rib 21 is surrounded by such metal, whereby the band is so completely mechanically interlocked with the body of the piston against any movement relative thereto at any part of the contacting interface that no physical bond at the interface is necessary. The entire mass of the band is so divided up into portions of relatively small cross-section that it may be forced to yield elastically so as to expand and contract with the piston virtually as though integrally formed of the same metal, and the resistance of the band to such yielding is not concentrated in such locations -as to cause any significant 'distortion of the piston as it expands and contracts. On'the contrary, it seems to reduce the distortion of the piston that would otherwise be caused by the uneven distribution of metal in the side wall of the piston that is required to form wrist pin bearing bosses (not shown).

Asclearly shown in Figures 5 and 6, circumferentially spaced portions of both the upper and lower surfaces of the piston ring groove 17, constituting substantial portionsfof all three of those surfaces, are formed by the alloy of the 'body of the piston, thus facilitating heat transfer between the piston ring (notshown) and'the sidewall of the piston. Also, by reason of the'relatively small cross-section of the bandit) in radial planes, over much theigreater part of 'theicircurnference' of the band, heat transfer downwardly from the hothead portion 23 ofthej p'iston into the more readily cooled sidewall portion below the band 'is offered minimum'resistance'by the massof the band. 'While'having the aforementioned attributes, the *carrier band '10 also forms the outer portions of the upper and lower sidewalls of the ring :groove 17 entirely about the circumference of'the piston. Thus, avhard wearing surface is provided .in contact with the ',piston.ring throughout the area of .contact where wear is normally concentrated.

,Fi'gures7 and 8 show a blank 25, suitablyformed as a casting, from which the carrier band 10 of Figures l-6 maybe ground or machined. 'Thedepressions 11 and protuberances 21 are all ,the same as in'the' finished'band ofjEigures 1-'-6. However,.the radial .width of'the blank between theinnersurface'lZ and the original outer surfaces 26 thereof is somewhat greater, by inchor so, than the corresponding dimension-of the 'finallcarrier band 10, .to permit machining toaccurate final dimensions and concentricity. Also,ra peripheral groove 27 that is somewhat narrower-and, shallower'than the final ring groove 17 of the Figures l-6 is preferably formed in'the'blanklZS ascast. The initial groove 27 may stop short of piercing through the blank into therecessesll, as shown in.Figures 79, or it maybe castto an initialfdepth suflicient to pierce through the blank,as.shown in.Figures ,l,6, but just .shortof the-final depth .to permit final. machiningpf "IQ W2 the bottom of the groove. This groove '27 decreases the volume of the band and thereby reduces its chilling effect on the piston metal as it is cast. It also seems to contribute to better flow of metal about the band when the groove 27 pierces through the blank into the scallop-like recesses 11, possibly by facilitating escape of entrapped gas. The groove 27 also conveniently serves to receive mold pins 28 or other supporting means for supporting the blank in the mold (not shown) while casting a rough piston 30 about the blank 25 (Figures 7 and 9). The pins 28 are of a diameter substantially as great as the width of the groove 27, and they may project into this groove substantially to the bottom thereof, as indicated in Figure 9. The width of the final ring groove 17 and the depth to which it is machined after the piston has been cast is shown in dotted outline in Figure 9. Also, the diameter of the rough piston 30 and, to the same degree, the diameter of the embedded blank 25, are reduced approximately /8 inch or so in final machining and/or grinding operations which convert the rough piston 30 (Figure 9) to the final piston 22 (Figures 5 and 6). v

The cheapness of a plain cast iron blank 25, the simplicity of the process of simply casting the piston metal about the blank, and the conventional ring groove and piston finishing operations required to produce the final product of Figures 5 and 6 provide substantial economies while achieving the desired operative and novel physical characteristics of the final piston discussed above. It will be seen, therefore, that the invention fulfills its several objects with the various advantages pointed out above in a simple and commercially practical manner.

While the invention has been illustrated herein by disclosing in considerable detail the presently preferred forms thereof, it will be appreciated that such details may be varied considerably and in various respects without departing from the principles of the invention or the scope thereof as defined in the appended claims.

Having disclosed our invention, we claim:

1. A hollow, cast metal piston having a top wall and a cylindrical side wall, and a cireumferentially continuous piston ring carrier band embedded in said side wall and substantially flush with the outer surface thereof, said band being formed of a different metal and shaped to provide a first circumferential array of spaced, scalloplike depressions extending radially and axially into the band from the inner and top surfaces thereof and a second circumferential array of spaced, scallop-like depressions similarly extending into the band from the inner and bottom surfaces thereof, said second array of depressions being cireumferentially staggered relative to said first set, the metal of said piston entering said depressions, and a circumferential piston ring groove extending radially into said band and through the band into the metal of the piston in the regions of said depressions, each of said depressions, over substantially the entire areas thereof in a plane transverse to the axis of the band, extending axially into the band more than half the axial thickness thereof.

2. A hollow, cast metal piston having a top wall and a cylindrical side wall, and a cireumferentially continuous piston ring carrier band embedded in said side wall and substantially flush with the outer surface thereof, said band being formed of a different metal and shaped to provide a first circumferential array of spaced, scalloplike depressions extending radially and axially into the band from the inner and top surfaces thereof and a second circumferential array of spaced, scallop-like depressions similarly extending into the band from the inner and bottom surfaces thereof, said second array of depressions being cireumferentially staggered relative to said first set, the metal of said piston entering said depressions, and a circumferential piston ring groove extending radially into saidband and through the band into the metal of the piston in the regions of said depressions, each of said depressions in one set being of less circumferential extent than the spacing of the depressions in the other set and being separated therefrom by intervening band portions forming side walls of said depressions, the circumferential extent of said side intervening band portions being small relative to the circumferential extent of said depressions, and said depressions, over substantially the entire areas thereof in a plane transverse to the axis of the band, extending axially into the band more than half the axial thickness thereof.

3. A hollow, cast metal piston having a top wall and a cylindrical side wall, and a cireumferentially continuous piston ring carrier band embedded in said side wall and substantially flush with the outer surface thereof, said band being formed of a different metal and shaped to provide a first circumferential array of spaced, scalloplike depressions extending radially and axially into the band from the inner and top surfaces thereof and a second circumferential array of spaced scallop-like depressions similarly extending into the band from the inner and bottom surfaces thereof, said second array of depressions being cireumferentially staggered relative to said first set, the metal of said piston entering said depressions, and a circumferential piston ring groove extending radially into said band and through the band into the metal of the piston in the regions of said depressions, the axial depth of said depressions increasing from the radially outer limits thereof toward the inner surface of the band, the depth thereof in any radial plane therethrough being greater than half the axial thickness of the band, and

the radial depths of said depressions being defined by generally cylindrical side walls giving them scallop-like configurations in a common plane transverse to the axis of the band.

4. A hollow, cast metal piston having a top wall and a cylindrical side wall, and a cireumferentially continuous piston ring carrier band embedded in said side wall and substantially flush with the outer surface thereof, said band being formed of a different metal and shaped to provide a first circumferential array of spaced, scalloplike depressions extending radially and axially into the band from the inner and top surfaces thereof and a second circumferential array of spaced, scallop-like depressions similarly extending into the band from the inner and bottom surfaces thereof, said second array of depressions being cireumferentially staggered relative to said first set, the metal of said piston entering said depressions, and at least one circumferential array of spaced, rib-like protuberances extending axially from said band, each of said protuberances being disposed between an adjacent pair of said depressions in circumferential alignment therewith and being embedded in said side wall of the piston.

5. A hollow, cast metal piston having a top wall and a cylindrical side wall, and a cireumferentially continuous piston ring carrier band embedded in said side wall and substantially flush with the outer surface thereof, said band being formed of a different metal and shaped to provide a first circumferential array of spaced, scalloplike depressions extending radially and axially into the band from the inner and top surfaces thereof and a second circumferential array of spaced, scallop-like depressions similarly extending into the band from the inner and bottom surfaces thereof, said second array of depressions being cireumferentially staggered relative to said first set, the metal of said piston entering said depressions, and at least one circumferential array of rib-like protuberances extending axially from said band, each of said protuberances being disposed between an adjacent pair of said depressions and spaced radially inwardly from the outer surface of said piston side Wall and being entirely embedded in the metal of the piston.

6. A hollow, cast metal piston having a top wall and a cylindrical side wall, and a cireumferentially continuous piston ring carrier band embedded in said Side wall and substantially flush with the outer surfacethereof, saidband being formed of a different metal and shaped to Pl'ovide a first circumferential array of spaced, scalloplike. epressions. extending radially and axially into the band from the inner and top Surfaces thereof and a second circumferential array of spaced, scallop-like. depressions similarly extending into. the band from the inner and bottom surfaces thereof, said second array of depressions being circumferentially staggered relative to said first set, the metal of said piston entering said depressions, a first circumferential array of rib-like protuberance extending axially from the top surface of said band, and a second array of rib-like protuberances extending axially from the bottom surface of said band, each of said pro,- tuberances being disposed between an adjacent pair of oppositely extending depressions and being entirely embedded in the metal of the piston.

7. A generally annular piston ring carrier band blank adapted to be embedded in the side wall of a piston, said blank having generally parallel upper and lower surfaces and generally concentric inner and outer surfaces, and being shaped to provide a first circumferential array of spaced, scallop-like depressions extending axially and radially into the blank from said upper and inner surfaces and a second circumferential array of spaced, scalloplike depressions similarly extending into the blank from said lower and inner surfaces, said second set of depressions being circumferentially staggered relative to said first set, each of said depressions, over substantially the entire areas thereof in a plane transverse to the axis of the band, extending axially into the blank more than half the axial thickness thereof between said upper and lower surfaces, and a circumferential groove extending into said blank from said outer surface.

8. A generally annular piston ring carrier band blank adapted to be embedded in the side wall of a piston,

said blank having generally parallel upper and lower surfaces and generally concentric inner and outer surfaces, and being shaped to provide a first circumferential array of spaced, scallop-like depressions extending axially and radially into the blank from said upper and inner sur-. faces and a second circumferential array of spaced, scallop-like depressions similarly extending into the blank from said lower and inner surfaces, said second set of depressions being circumferentially staggered relative to said first set, each of said depressions over substantially the entire areas thereof in a plane transverse to the axis of; the band, extending axially into the blank more than half the axial thickness thereof between said upper and lower surfaces, and a circumferential groove extending into said blank from said outer surface to, a depth short of said depressions,

9. A generally annular piston ring carrier band blank adapted to be embedded in the side wall of a piston, said blank having generally parallel upper and lower surfaces and generally concentric inner and outer surfaces, and being shaped to provide a first circumferential array of spaced, scallop-like depressions extending axially :and radially into the blank from said upper and inner surfaces and a second circumferential :array of spaced, scalloplike depressions similarly extending into the blank from said lower and inner surfaces, said second set of depressions being ciroumferentially staggered relative to said first set, each of said depressions, over substantially the entire areas thereof in a plane transverse to the axis of the an ex endi g a ally in o the l k m re. than half the axial thickness thereof between said upper and lower surfaces, and a circumferential groove extending into said blank from said outer surface to a depth piercing through the blank into said depressions.

10. A generally annular piston ring carrier band blank adapted to be embedded in the side wall of a piston, said blank having generally parallel upper and lower surfaces and generally concentric inner and outer surfaces, and eing shaped to provide a first circumferential array of space scallcp-lik depressions extending axially and ra-v ial y in he bl nk. from. sai upp r an n r rfa es and a second cir umferentia ar y of Spaced, c llop ke d press on sim la y e nding into the lank r m aid lower and. inner sur a es, said eco set f. epr sions being cireurnferentially staggered relative to said first set, each of said depressions, over substantially the entire area; thereof in a plane transverse to the axis of the band, extending axially into the blank more than half the. axial thickness thereof between said upper and lower surfaces, a circumferential groove extending into said blank from said outer surface, and at least one circumferential array of spaced, rib-like protuberances extending axially from said blank, each of; saidribs being disposed between an adjacent pair of said depressions and being spaced radially between said inner and outer surfaces in circumferential alignment with said adjacent depressions.

11. A generally annular piston ring carrier band blank adapted to be embedded in the side wall of a piston, said blank having generally parallel upper and lower surfaces and generallyconcentric inner and outer surfaces, and being shaped to provide a first circumferential array of spaced, scallop-like depressions extending axially and radially into the blank from said upper and inner surfaces and a second circumferential array of spaced, scallop-like depressions similarly extending into the blank from said lower and inner surfaces, said second set of depressions being circumferentially staggered relative to said first set, each of said depressions, over substantially the entire areas thereof in a plane transverse to the axis of the band, extending axially into. the blank more than half the axial thickness thereof between said upper and lower surfaces, a circumferential groove extending into said blank from said outer surface to a depth short of said depressions, and at least: one circumferential array of spaced, rib-like protuberances extending axially from said blank, each of said ribs being disposed between an adjacent pair of said depressions and being spaced radially between said in: ner and outer surfaces in circumferential alignment with said adjacent depressions.

2- A gen rally ann la p s on ring carrier b n blank. adapted to be embedded in the side wall of a piston, said blank having generally parallel upper and lower surfaces and generally concentric inner and outer surfaces, and being shaped to provide a first circumferential are ray of spacedpscallop-like depressions extending axially nd radia ly in o he blank from aid pp r n i ner ur aces and a second circumfe n al array f spaced,

scallop-like depressions similarly extending into the blank from said lower and inner surfaces, said secondset of depressions being circumferentially staggered relative to said first set, each of said depressions, over substantially the en a tire areas thereof in a plane. transverse to the axis of the band, extending axially into the blank more than half the axial thickness thereof between said upper and lower surfaces, a circumferential groove extending into said blank from said outer surface to a depth piercing through said blank into said depressions, and at least one circumferential array of spaced, rib-like protuberances extending ax-. ially from said blank, each of said ribs being disposed between an adjacent pair of said depressions and being spaced radially between said inner and outer surfaces in circumferential alignment with said adjacent depressions.

References Cited in the file of this patent UNITED STATES PATENTS 1,742,795 Tanner Jan. 7, 1930 2,685,729 Daub Aug. 10, 1954 2,707,136 Fahlman Apr. 26, 1955 OTHER REFERENCES Automotive Industries, volume No. 105, issue No. 9, published Nov. 1, 1951 (see inside back cover).

SAE Journal, volume No. 61, issue No. 10, published Oct. 1953, pages 34-35. 

